Inverse Barometer correction comparison for TOPEX/Poseidon mission between Corrections based on JRA-55 and ERA-Interim atmospheric reanalyses

Transcription

1 Inverse Barometer correction comparison for TOPEX/Poseidon mission between Corrections based on JRA-55 and ERA-Interim atmospheric reanalyses The JRA-55 correction is referred to as JRA55 in the following study The ERA-Interim correction is referred to as ERA Lionel Zawadzki, Michael Ablain (CLS)

2 Introduction: Inverse Barometer correction comparison for TOPEX/Poseidon mission We will observe and analyse the impact of the Inverse Barometer correction computed from the JRA- 55 atmospheric reanalysis for climate applications on the TOPEX/Poseidon period We will compare this correction with the Inverse Barometer correction computed from the ERA-Interim atmospheric reanalysis. It will be referred to as ERA. In order to determine the impact of this alternative Inverse Barometer correction in terms of climate applications and temporal scales, we will try in this study to indicate for each impact detected if it s a positive (+) or a negative (-) impact : Low impact Significant impact No impact detected

3 Global Mean Sea Level Climate Applications Global Mean Sea Level Regional Mean Sea Level Mesoscale Temporal Scales Inter annual signals (> 1 year) < 2 months TOPEX/Poseidon Round Robin Data Package (RRDP) JRA55 Versus ERA Low impact detected on Global Mean Sea Level trend 0.05 mm/yr on the Global MSL is significant. Temporal of SLA mean calculated globally.

4 Global Mean Sea Level Climate Applications Global Mean Sea Level Regional Mean Sea Level Mesoscale Temporal Scales Inter annual signals (> 1 year) < 2 months TOPEX/Poseidon Round Robin Data Package (RRDP) JRA55 Versus ERA No impact detected on Inter annual The figure below shows the mean difference between the two corrections calculated globally by cycle.

5 Global Mean Sea Level Climate Applications Global Mean Sea Level Regional Mean Sea Level Mesoscale Temporal Scales Inter annual signals (> 1 year) < 2 months TOPEX/Poseidon Round Robin Data Package (RRDP) JRA55 Versus ERA Low impact detected on Semi-annual

6 Mesoscale Climate Applications Global Mean Sea Level Regional Mean Sea Level Mesoscale Temporal Scales Inter annual signals (> 1 year) TOPEX/Poseidon Round Robin Data Package (RRDP) JRA55 Versus ERA < 2 months - Significant impact detected on a short temporal scale (signals < 2 months): Crossovers Variance Differences are generally positive (see figures on next slide) between 0 and -1 cm² : this means that the Inverse Barometer correction based on JRA55 shows degradations by comparison to the ERA- Interim correction. The map of SSH crossovers Variance Differences shows that these degradations are mainly below -50 latitude.

7 Mesoscale Map of Variance differences of Sea Surface Height at crossovers between the Inverse Barometer based on JRA55 and ERA-Interim (over all the period): - significant degradation at high latitudes, below -50 Temporal of Variance differences of Sea Surface Height at crossovers between two Inverse barometer corrections : - Significant degradation (~0.5cm²)

8 Regional Mean Sea Level Climate Applications Global Mean Sea Level Regional Mean Sea Level Mesoscale Temporal Scales Inter annual signals (> 1 year) < 2 months TOPEX/Poseidon Round Robin Data Package (RRDP) JRA55 Versus ERA Significant impact detected on Regional Mean Sea Level We observe a significant impact (1 mm/yr) on the regional trends near coasts and ~0.5mm/yr in the open ocean, mainly in the Pacific.

9 Regional Mean Sea Level Map of Sea Level Anomaly differences between two JRA55 corrections (over all the period)

10 Regional Mean Sea Level Climate Applications Global Mean Sea Level Regional Mean Sea Level Mesoscale Temporal Scales Inter annual signals (> 1 year) < 2 months TOPEX/Poseidon Round Robin Data Package (RRDP) JRA55 Versus ERA Low impact detected on Semi-Annual Amplitude differences reach 2mm or 2mm for annual and signal (see figures on next slide). A North/South hemispheres difference is visible The corresponding phase shifts are low (about 10 days=1cycle)

11 Regional Mean Sea Level Map of Sea Level Anomaly differences amplitude for annual signal Map of Sea Level Anomaly differences amplitude for signal SLA with JRA55 amplitude SLA with ERA amplitude : annual signal SLA with JRA55 amplitude SLA with ERA amplitude : signal

12 Regional Mean Sea Level Map of Sea Level Anomaly differences phase for annual signal. Map of Sea Level Anomaly differences phase for signal. To be noted a phase value equal to 30 corresponds to a period of one month SLA with JRA55 phase SLA with ERA phase: annual signal SLA with JRA55 phase SLA with ERA phase : signal

13 Regional statistics between corrections Map of Mean differences between JRA55 and ERA (extension period) On this map we observe clearly differences near coast, up to +4mm. Map of Standard deviation differences between JRA55 and ERA (extension period) On this map we observe differences mainly near coasts

14 Inverted Barometer correction comparison for TOPEX/Poseidon mission To conclude: The Inverted Barometer (IB) correction based on the JRA55 atmospheric reanalysis shows degraded performances by comparison to the IB based on ERA- Interim The degradations are mainly at crossovers Main impact is on the long-term s at regional scale Significant differences near coasts Climate Applications Global Mean Sea Level Regional Mean Sea Level Mesoscale Temporal Scales Inter annual signals (> 1 year) TOPEX/Poseidon Round Robin Data Package (RRDP) JRA55 Versus ERA < 2 months -